Mold structures for continuously casting an elongated metal body of desired cross-section



E. PIPITZ ET AL 3,414,046 'URES FOR CONTINUOUSLY CASTING AN ELONGATED AL BODY OF DESIRED CROSS-SECTION Filed Nov. 23, 1965 Dec. 3, 1968 MOLD STR C United States Patent 3,414,046 MOLD STRUCTURES FOR CONTINUOUSLY CAST- ING AN ELONGATED METAL BODY OF DE- SIRED CROSS-SECTION Egon Pipitz and Gerolf Strohmeier, Reutte, and Bruno Tarmann, Kapfenberg, Austria, assignors to Schwarzkopf Development Company, New York, N.Y., a corporation of New York, and Gebr. Bolder & Company, Kapfenberg, Austria, a corporation of Austria Filed Nov. 23, 1965, Ser. No. 509,422 Claims priority, application Austria, Dec. 10, 1964, A 10,478/64 6 Claims. (Cl. 164273) This application. is based and claims the priority of the corresponding application filed in Austria on Dec. 10, 1964.

This invention relates to mold structures or mold section of a continuous casting apparatus which continuously receives molten corrosive metal and continuously forms successive solidified body sections of an elongated body having a predetermined cross-section which are delivered to successive parts or sections of such continuous casting apparatus.

The materials heretofore used for the permanent mold section of such continuous casting apparatus have only limited life. As an example, copper which is usually used for such permanent mold section has high electric con ductivity and suppresses the rotating magnetic fields used for regulating the flow of the continuously supplied molten metal. This limitation also applies to copper-chromium alloys. Although brass and aluminum will not suppress the rotary magnetic field, they deteriorate and have a very short life and strongly impair the economic value of such continuous metal casting process.

Among the objects of the invention is a hollow shapegiving mold for a continuous steel casting apparatus which enables continuous shaping of a continuously cast elongated steel body of predetermined cross-section for a much longer time than heretofore possible.

In accordance with the invention hollow molds for such continuous-casting apparatus are made with a metal ceramic composition wherein 85 to 20 vol. percent is a metal phase consisting of molybdenum or tungsten and to 80 vol. percent of a ceramic phase consisting of zirconium oxide stabilized with 4 to 10' wt. percent of magnesium oxide or calcium oxide or both of these additional oxides. Up to 50 wt. percent of the zirconium oxide may be replaced with thorium oxide or hafnium oxide or titanium oxides or their mixtures.

The single figure is a cross-sectional view of a mold of the invention having a shape-giving interior of a known prior-art mold.

As stated above, shape-giving molds of continuous casting apparatus having a life much longer than prior molds by forming of a sintered powder particle body combining 85 to vol. percent of metal phase consisting of molybdenum or tungsten with 15 to 80 vol. percent, zirconium oxide stabilized with 4 to 10 wt. percent of magnesium oxide and/or calcium oxide.

The mold 10 has an upper edge 11 and a lower edge 12. The still molten steel reaching the upper mold opening is cooled as it passes the hollow mold interior and the cross-section of the lower mold end gives the discharged solidifying steel body the desired shaped cross-section. The mold is made by known powder-metallurgic techniques of the metal-ceramic compositions of the invention.

As an example, there will now be described the process of forming a permanent mold section for such continuous casting apparatus used in making a continuous length of a hollow shaped metal rod or bar, which in the specific ex- "ice 7 diameter. The specific mold section is 7.5 centimeters long, has an inner diameter of 8 centimeters and a Wall thickness of 1 centimeter. There was prepared an intimate fine powder mixture consisting of 60 vol. percent molybdenum, 35 vol. percent zirconium oxide and 5 vol. percent magnesium oxide. This powder mixture was hydrostatically compressed into a self-supporting compact of the above-specified cylindrical mold shape. The compact was then subjected to an initial sintering operation at 1200 C. followed by cooling, both in. a hydrogen. The presintered compact was then machined as by drilling to the desired final mold shape. The machined presintered compact was thereafter given the final sintering operation at 2000 C. in hydrogen. By etching the exposed mold surfaces, as with nitrohydrochloric acid, the metal content of such exposed surface layer was removed thereby providing the mold with an exposed surface layer consisting of a zirconium oxide base ceramic skeleton free from metal and not readily wetted by molten steel.

In accordance with the invention, different parts of such shape-giving mold may be formed with different compositions. As an example, the upper part of such mold, which is subjected under greater thermal strain by the inflowing molten metal, is formed with 40 vol. percent molybdenum, 53.5 vol. percent zirconium oxide and 6.5 vol. percent magnesium oxide. The lower part of this mold which is subjected to only moderate temperature has a much larger metal phase or is formed in its entirety of metal.

Molds formed of compositions of the invention containing 85 to 20 vol. percent of the metal phase and balance the ceramic phase have a much longer useful life as the critical part of a continuous metal casting apparatus. This is also assured because these compositions of the invention have a relatively low thermal expansion coeificient and relatively good thermal conductivity. Such molds have also the property of enabling passage therethrough or of being permeable by rotary or alternating magnetic fields. When used for casting continuously formed metallic rods, such molds exhibit great strength and corrosion resistance to discharged and streaming molten metal at high temperatures, thereby assuring that the continuously produced metal rod is of good quality being formed with the desired cross-section and being free of longitudinal fissures.

In the heretofore used continuous casting apparatus, the discharged molten metal starts solidifying at the casting surface level of the cast metal. As a result, the casting surface is, in some cases, contaminated by liquid or pulverized slag. This makes is necessary to perform the continuous casting operation at low speeds, such as centimeters per second, which for technical and economic reasons is possible only when casting long bodies of large cross-section. In contrast, in continuous casting with a hollow casting mold formed with compositions of the invention which resist corrosion by streaming molten steel, a steel rod of the desired cross-section may be continuously formed at much greater speed. A closed] casting mold may be used in such operation to assure that the solidification of the cast molten steel starts only at a desired predetermined distance from the casting surface of the continuously cast metal. This heretofore not used casting procedure has many advantages, including suppression of oxidation of the cast molten metal and avoidance of the solidification of the cast molten metal at the casting surface level. Such avoidance of the solidification of the cast molten metal is of great importance in systems where a continuously cast steel or steel alloy rod is formed with a horizontal continuous casting process. Heretofore such continuous casting could only be performed with a casting mold of graphite. Although such graphite mold enables continuous casting of iron, it cannot be used for continuous casting of steel because the graphite of such mold dissolves in the molten steel. Similar advantages in securing delayed solidification of the cast metal are achieved with molds of the invention when used in a vertically cast continuous casting process.

The inlet section of such closed casting mold of the invention may also be combined with several branching mold sections to which the continuously cast metal is delivered for further processing. Such system may be com bined with control means for regulating the delivery of the cast metal to the different branching mold sections.

Casting molds of the invention for continuous metal casting systems may also be produced with a curved mold passage thereby enabling curved casting on an economic basis.

It should be noted that the metalic phase of the just described hollow casting mold may contain chromium up to 50 percent of its weight.

The principles underlying specific examples of the invention described above will suggest other modifications thereof. It is accordingly desired that the appended claims shall not be limited to specific examples shown or described herein.

There is claimed:

1. A hollow mold structure of a continuous casting apparatus for continuously casting an elongated metal body,

which mold structure has a mold section of predetermined cross-section shaped to continuously receive molten corrosive metal through an inlet opening and at least partially solidifying the received molten metal into successive solidified body portions of said elongated metal body having said cross-section, said mold section having an outlet end shaped to feed said successive solidified metal body portions to succeeding sections of said casting apparatus,

said mold structure consisting of a hard homogenous composition consisting of a ceramic phase and a metal phase,

said ceramic phase constituting 80 to vol. percent of said mold structure and consisting of a ceramic selected from the group consisting of zirconium oxide containing 4 to 10 wt. percent of calcium oxide, zirconium oxide containing 4 to 10 wt. percent of magnesium oxide, such zirconium oxides containing up to 50 wt. percent thorium oxide, such zirconium oxides containing up to 50 wt. percent titanium oxide, such zirconium oxides containing up to 50 wt. percent hafnium and combinations of two and more of said ceramics,

said metalic phase constituting to 85 vol. percent of and being the balance of said mold structure and consisting of metal selected from the group consisting of molybdenum, tungsten, molybdenum containing up to 50 Wt. percent chromium, tungsten containing up to 50 Wt. percent chromium, a tungsten-molybdenum alloy containing up to 50 wt. percent chromium and alloys of two and more of said metals,

said mold structure consisting of a homogenous mixture of fine powder particles of said specified ceramic and metal phase ingredients, which particles have been compacted and have been sintered at temperatures of at least 1800 C into a homogenous body having a high density near the theoretical density of its composition and resisting corrosion by molten metal at high temperatures of at least about 1400 C. in contact therewith. 2. A hollow mold structure of a continuous casting apparatus as claimed in claim 1,

the surface layer of said mold section exposed at said temperatures to said corrosive molten metal being free of said metal phase and being formed solely of said ceramic phase ingredients and exhibiting wetting resistance to said molten metal at said high temperature. 3. A hollow mold structure of a continuous casting apparatus as claimed in claim 1, a

the surface layer of said mold section exposed at said temperatures to said corrosive molten metal being free of said metal phase and being formed solely of said ceramic phase ingredients and exhibiting wetting resistance to said molten metal at said high temperature, said ceramic phase being 60 to 40 vol. percent and said metal phase being 40 to 60 vol. percent of said shaped body. 4. A hollow mold structure of a continuous casting apparatus as claimed in claim 1,

said ceramic phase being 60 to 40 vol. percent and said metal phase being 40 to 60 vol. percent of said shaped body. I 5. A hollow mold structure of a continuous casting apparatus as claimed in claim 2,

the surface layer of said mold section exposed at said temperatures to said corrosive molten metal being free of said metal phase and being formed solely of said ceramic phase ingredients and exhibiting wetting resistance to said molten metal at said high temperatures. 6. A hollow mold structure of a continuous casting apparatus as claimed in claim 2,

the surface layer of said mold section exposed at said temperatures to said corrosive molten metal being free of said metal phase and being formed solely of said ceramic phase ingredients and exhibiting wetting resistance to said molten metal at said high temperature said ceramic phase being 60 to 40 vol. percent and said metal phase being 40 to 60 vol. percent of said mold structure.

References Cited UNITED STATES PATENTS 2,747,260 5/1956 Carlton et al. -206 X 2,798,808 7/1957 Iredell et al. 75206 3,158,473 11/1964 Gatti 75206 3,181,947 5/1965 Vordahl 75206 3,222,148 12/1965 Hay 10657 X 3,264,694 8/1966 Weber 10657 X J. SPENCER OVERHOLSER, Primary Examiner.

E. MAR, Assistant Examiner. 

1. A HOLLOW MOLD STRUCTURE OF A CONTINUOUS CASTING APPARATUS FOR CONTINUOUSLY CASTING AN ELONGATED METAL BODY, WHICH MOLD STRUCTURE HAS A MOLD SECTION OF PREDETERMINED CROSS-SECTION SHAPED TO CONTINUOUSLY RECEIVE MOLTEN CORROSIVE METAL THROUGH AN INLET OPENING AND AT LEAST PARTIALLY SOLIDIFYING THE RECEIVED MOLTEN METAL INTO SUCCESSIVE SOLIDIFIED BODY PORTIONS OF SAID ELONGATED METAL BODY HAVING SAID CROSS-SECTION, SAID MOLD SECTION HAVING AN OUTLET END SHAPED TO FEED SAID SUCCESSIVE SOLIDIFIED METAL BODY PORTIONS TO SUCCEEDING SECTIONS OF SAID CASTING APPARATUS, SAID MOLD STRUCTURE CONSISTING OF A HARD HOMOGENOUS COMPOSITION CONSISTING OF A CERAMIC PHASE AND A METAL PHASE, SAID CERAMIC PHASE CONSTITUTING 80 TO 15 VOL. PERCENT OF SAID MOLD STRUCTURE AND CONSISTING OF A CERAMIC SELECTED FROM THE GROUP CONSISTING OF ZIRCONIUM OXIDE CONTAINING 4 TO 10 WT. PERCENT OF CALCIUM OXIDE, ZIRCONIUM OXIDE CONTAINING 4 TO 10 WT. PERCENT OF MAGNESIUM OXIDE, SUCH ZIRCONIUM OXIDES CONTAINING UP TO 50 WT. PERCENT THORIUM OXIDE, SUCH ZIRCONIUM OXIDES CONTAINING UP TO 50 WT. PERCENT TITANIUM OXIDE, SUCH ZIRCONIUM OXIDES CONTAINING UP TO 50 WT. PERCENT HAFNIUM AND COMBINATIONS OF TWO AND MORE OF SAID CERAMICS, SAID METALIC PHASE CONSTITUTING 20 TO 85 VOL. PERCENT OF AND BEING THE BALANCE OF SAID MOLD STRUCTURE AND CONSISTING OF METAL SELECTED FROM THE GROUP CONSISTING OF MOLYBDENUM, TUNGSTEN, MOLYBDENUM CONTAINING UP TO 50 WT. PERCENT CHROMIUM, TUNGSTEN CONTAINING UP TO 50 WT. PERCENT CHROMIUM, A TUNGSTEN-MOLYBDENUM ALLOY CONTAINING UP TO 50 WT. PERCENT CHROMIUM AND ALLOYS OF TWO AND MORE OF SAID METALS, SAID MOLD STRUCTURE CONSISTING OF A HOMEGENOUS MIXTURE OF FINE POWDER PARTICLES OF SAID SPECIFIED CERAMIC AND METAL PHASE INGREDIENTS, WHICH PARTICLES HAVE BEEN CONPACTED AND HAVE BEEN SINTERED AT TEMPERATURES OF AT LEAST 1800*C INTO A HOMOGENOUS BODY HAVING A HIGH DENSITY NEAR THE THEORETICAL DENSITY OF ITS COMPOSITION AND RESISTING CORROSION BY MOLTEN METAL AT HIGH TEMPERATURES OF AT LEAST ABOUT 1400* C. IN CONTACT THEREWITH. 